Scientists from Brazilian institutions, in collaboration with researchers from Israel, “manipulated” carbon nanotubes of 1 nm diameter deposited on quartz surfaces and analyzed strain and displacements produced by this nanointervention. The team identified some behavior patterns in the nanotubes – quartz system and formulated a mathematical model applicable to systems formed by one- and two-dimensional materials over various substrates. The results of the study were recently published in Nano Letters.

To perform the experiments, the Brazilian investigators used samples idealized and produced in the Weizmann Institute of Science (Israel), in which the nanotubes are serpentine-shaped (composed of parallel segments connected together by U-shaped curves).These samples offered a desirable complexity, fostered by both the nanotubes format and the anisotropic character of quartz, which makes adhesion of nanotubes to the substrate not the same at all points.

In order to “manipulate” the system, the researchers used the tip of an atomic force microscope (AFM) built in the laboratory, which allows to change the position of nanometric particles and even of atoms, and to measure in situ the optical spectrum of nanostructures. In each sample, the tip touched a point of the quartz substrate and pushed toward the nanotube, and then proceeded to the optical analysis.

Before and after nanomanipulation, the scientists analyzed a number of points in the nanotube using the technique of Raman spectroscopy, which provides information about the frequency in which the atoms vibrate in the area being studied. More specifically, researchers focused on the frequency of the “G band”, which is used to infer the strain measurements of a considered point, since changes in the frequency of the “G band” are proportional to changes in strain.

Thus, scientists were able to identify and analyze different behavior of the nanotubes after nanomanipulation; for example, the detachment of the substrate and the intense displacement of a full stretch of the nanotube that had received two manipulations at the same point.

In addition to performing the experimental work, the authors of the article in Nano Letters managed to condense the complexity of behaviors they observed in a mathematical model (an equation) capable of explaining them theoretically and predicting these phenomena in similar systems. “The paper proposes a relatively simple model to describe complex effects of nanostructures adhesion in support media,” says Ado Jório, professor in the Department of Physics of the Federal University of Minas Gerais (UFMG) signing the letter as corresponding author.

The research that led to the Nano Letters article was developed within the master’s, doctoral and postdoctoral work of three authors of the letter, in the context of the Brazilian Network for Research and Instrumentation in Optical Nano-Spectroscopy, a project funded by the National Council for Scientific and Technological Development (CNPq) and coordinated by Ado Jório. “This is the result of a broad scientific instrumentation project, which aims at reaching the level of manipulating nanostructures and measuring, accurately, the effect of this process at the nanoscale,” says Jório.

The figure shows one of the 34serpentine-shaped nanotubes on crystalline quartz substrate studied by the authors of the article. To the left of the reader is the nanotube before manipulation. To the right, following the sequence, the same nanotube after the intervention, with the consequent evident strain. The central segment of the nanotube, where the nanomanipulation occurred, was colorized, the gray scale indicating the frequency of the G band in that place. Finally, farther to the right, the chart displays the frequency of G band measured by Raman spectroscopy in successive points of this nanotube (graphical representation of gray hues): the black circles refer to non-manipulated nanotube and the gray colored circles, to the manipulated ones.